Tesla's Giga-Plan Looks Too Ambitious

Yes, Elon Musk's plan to build a huge factory to dramatically trim the cost of lithium battery packs could work. But there's a very big catch.

Electric-car maker Tesla Motors has grabbed the attention of the auto industry, the electronics industry, and of course, the stock market, where the company's shares reached $265 a month ago, as Tesla's chief, Elon Musk, outlined his daring plan to build the world's biggest lithium-ion battery factory.

Even after falling back almost 20% since then, the stock values the company at more than $30 billion (counting shares issuable for options and convertible debt). That's more than 100% over the level at which this tabloid...